Thursday, December 7, 2017

More Data Narrows Primordial Black Hole Dark Matter Parameter Space

Black hole merger events detected by the Laser Interferometer Gravitational-Wave Observatory (LIGO) have revived dark matter models based on primordial black holes (PBH) or other massive compact halo objects (MACHO). This macroscopic dark matter paradigm can be distinguished from particle physics models through their gravitational lensing predictions: compact objects cause most lines of sight to be demagnified relative to the mean, with a long tail of higher magnifications. We test the PBH model using the lack of lensing signatures on type Ia supernovae (SNe), modeling the effects of large scale structure, allowing for a non-gaussian model for the intrinsic SNe luminosity distribution and addressing potential systematic errors. Using current JLA (Union) SNe data, we derive bounds ΩPBH/ΩM<0.346(0.405) at 95% confidence, ruling out the hypothesis of MACHO/PBH comprising the totality of the dark matter at 5.01σ(4.28σ) significance. The finite size of SNe limits the validity of the results to MPBH≳0.01M⊙, fully covering the black hole mergers detected by LIGO and closing that previously open PBH mass range.

The limiting minimal size of PBH covered by the exclusion, 0.01M⊙, is equivalent to about ten times the mass of Jupiter (which implies an event horizon of the Primordial Black Hole with a radius of approximately 28 meters, which would fit comfortably within a baseball field).

This is notable, because it makes previous MACHO/PBH exclusions more robust, but the sweet spot for MACHO dark matter was already limited to PBH objects with a mass on the order of the Moon (many hundreds of times less than the mass of Jupiter), and a event horizon radius on the order of millimeters.